This invention relates, in general, to semiconductor products and more particularly, to processing of semiconductor materials.
Conventionally, isolation of active areas on a semiconductor device is generally achieved by nonplanarizing methods, such as local oxidation of silicon (LOCOS). The LOCOS method, while achieving adequate isolation of active areas, does not satisfy a growing requirement for vertical sidewalls, planarity of both active areas and isolation areas, and potential for deeper isolation elements. These requirements for vertical sidewalls, greater planarity, and deeper isolation are driven by semiconductor devices that are smaller, denser, and that have a larger number of layers that are vertically stacked. Isolation with vertical sidewalls results in a lower parasitic capacitance, thereby resulting in better device performance. However, by not achieving planarity of the active areas and the isolation areas, problems result, such as wasting potential active area space, not being able to process subsequent layers by photolithographic and etch methods, as well as not being able to manufacture efficiently advanced semiconductor devices.
Several methods have been tried unsuccessfully to provide a high aspect ratio isolation with coplanar active areas and isolation areas, such as poly-buffered LOCOS, selective epitaxial growth, and polishing of dielectric materials. Each of these methods either does not achieve adequate planarity of the semiconductor device, results in unacceptable parasitic capacitance, or is so difficult that the method is not commonly used in manufacturing.
It can be seen that conventional isolation methods are not adequate for achieving planarity between the active areas and the isolation areas for manufacturing advanced semiconductor devices. Therefore, a method that would result in a planar active area and a planar isolation area would be highly desirable. Additionally, a method that not only achieves planarity, but also is inexpensive and is easy to implement would also be desirable.